Как то так?
split_content = (['@Book{Clark2003,',
'author , {Eve Clark},',
'title , {First Language Acquisition},',
'publisher , {Cambridge University Press},',
'address , {Cambridge, UK},',
'year , 2003}',
'volume , 10}}'],
['',
'@techreport{arrow1948,',
'author , {Arrow, Kenneth J.},',
'title , {The possibility of a universal social welfare function},',
'institution , {RAND Corporation},',
'year , {1948},',
'number , {P-41},',
'type , {Report}'])
asString_1 = ','.join(map(str,split_content[0]))
asString_2 = ','.join(map(str,split_content[1]))
aWord = 'Clark'
if(aWord in asString_1):
print("in the first element")
elif(aWord in asString_2):
print("in the second element")
#elif(...)
# ...